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Merged
Licenser merged 3 commits into from
Oct 4, 2026
Merged

Deserialize struct variants from a sequence in Value #488

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e0953ea
fix: reject extra array elements when deserializing from a Value
claude Oct 1, 2026
3350971
fix: deserialize struct variants from a sequence in Value
claude Oct 1, 2026
cf629f7
test: tuple variants from a Value reject extra elements
claude Oct 4, 2026
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47 changes: 41 additions & 6 deletions src/serde/value/borrowed/de.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,7 @@ impl<'de> de::Deserializer<'de> for Value<'de> {
Cow::Owned(s) => visitor.visit_string(s),
},

Value::Array(a) => visitor.visit_seq(Array(a.into_iter())),
Value::Array(a) => visit_array(Array(a.into_iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectAccess::new(o.into_iter())),
}
}
Expand Down Expand Up @@ -126,7 +126,7 @@ impl<'de> de::Deserializer<'de> for Value<'de> {
{
match self {
// Give the visitor access to each element of the sequence.
Value::Array(a) => visitor.visit_seq(Array(a.into_iter())),
Value::Array(a) => visit_array(Array(a.into_iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectAccess::new(o.into_iter())),
other => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Expand All @@ -142,7 +142,33 @@ impl<'de> de::Deserializer<'de> for Value<'de> {
}
}

/// Number of array elements not yet handed out.
trait Remaining {
fn remaining(&self) -> usize;
}

/// Hands the array to `visitor`; elements a fixed-length visitor (tuple, array, tuple struct) did
/// not read are an error, as with the text deserializer and serde's `SeqDeserializer`.
fn visit_array<'de, A, V>(mut seq: A, visitor: V) -> Result<V::Value, Error>
where
A: SeqAccess<'de, Error = Error> + Remaining,
V: Visitor<'de>,
{
let len = seq.remaining();
let value = visitor.visit_seq(&mut seq)?;
if seq.remaining() == 0 {
Ok(value)
} else {
Err(de::Error::invalid_length(len, &"fewer elements in array"))
}
}

struct Array<'de>(std::vec::IntoIter<Value<'de>>);
impl Remaining for Array<'_> {
fn remaining(&self) -> usize {
self.0.len()
}
}

// `SeqAccess` is provided to the `Visitor` to give it the ability to iterate
// through elements of the sequence.
Expand All @@ -160,6 +186,11 @@ impl<'de> SeqAccess<'de> for Array<'de> {
}

struct ArrayRef<'de>(std::slice::Iter<'de, Value<'de>>);
impl Remaining for ArrayRef<'_> {
fn remaining(&self) -> usize {
self.0.len()
}
}

// `SeqAccess` is provided to the `Visitor` to give it the ability to iterate
// through elements of the sequence.
Expand Down Expand Up @@ -565,7 +596,7 @@ impl<'de> VariantAccess<'de> for VariantDeserializer<'de> {
if v.is_empty() {
visitor.visit_unit()
} else {
visitor.visit_seq(Array(v.into_iter()))
visit_array(Array(v.into_iter()), visitor)
}
}
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Expand All @@ -589,6 +620,8 @@ impl<'de> VariantAccess<'de> for VariantDeserializer<'de> {
{
match self.value {
Some(Value::Object(o)) => visitor.visit_map(ObjectAccess::new(o.into_iter())),
// a struct variant may be written as a sequence, as when deserializing from text
Some(Value::Array(a)) => visit_array(Array(a.into_iter()), visitor),
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Some(other.value_type()),
Expand Down Expand Up @@ -623,7 +656,7 @@ impl<'de> de::Deserializer<'de> for &'de Value<'de> {
#[allow(clippy::useless_conversion)] // .into() required by ordered-float
Value::Static(StaticNode::F64(n)) => visitor.visit_f64((*n).into()),
Value::String(s) => visitor.visit_borrowed_str(s),
Value::Array(a) => visitor.visit_seq(ArrayRef(a.as_slice().iter())),
Value::Array(a) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
}
}
Expand Down Expand Up @@ -663,7 +696,7 @@ impl<'de> de::Deserializer<'de> for &'de Value<'de> {
{
match self {
// Give the visitor access to each element of the sequence.
Value::Array(a) => visitor.visit_seq(ArrayRef(a.as_slice().iter())),
Value::Array(a) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
other => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Expand Down Expand Up @@ -778,7 +811,7 @@ impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
if v.is_empty() {
visitor.visit_unit()
} else {
visitor.visit_seq(ArrayRef(v.as_slice().iter()))
visit_array(ArrayRef(v.as_slice().iter()), visitor)
}
}
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Expand All @@ -802,6 +835,8 @@ impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
{
match self.value {
Some(Value::Object(o)) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
// a struct variant may be written as a sequence, as when deserializing from text
Some(Value::Array(a)) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Some(other.value_type()),
Expand Down
47 changes: 41 additions & 6 deletions src/serde/value/owned/de.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@ impl<'de> de::Deserializer<'de> for Value {
#[allow(clippy::useless_conversion)] // .into() required by ordered-float
Value::Static(StaticNode::F64(n)) => visitor.visit_f64(n.into()),
Value::String(s) => visitor.visit_string(s),
Value::Array(a) => visitor.visit_seq(Array(a.into_iter())),
Value::Array(a) => visit_array(Array(a.into_iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectAccess {
i: o.into_iter(),
v: None,
Expand Down Expand Up @@ -114,7 +114,7 @@ impl<'de> de::Deserializer<'de> for Value {
{
match self {
// Give the visitor access to each element of the sequence.
Value::Array(a) => visitor.visit_seq(Array(a.into_iter())),
Value::Array(a) => visit_array(Array(a.into_iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectAccess::new(o.into_iter())),
other => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Expand All @@ -130,7 +130,33 @@ impl<'de> de::Deserializer<'de> for Value {
}
}

/// Number of array elements not yet handed out.
trait Remaining {
fn remaining(&self) -> usize;
}

/// Hands the array to `visitor`; elements a fixed-length visitor (tuple, array, tuple struct) did
/// not read are an error, as with the text deserializer and serde's `SeqDeserializer`.
fn visit_array<'de, A, V>(mut seq: A, visitor: V) -> Result<V::Value, Error>
where
A: SeqAccess<'de, Error = Error> + Remaining,
V: Visitor<'de>,
{
let len = seq.remaining();
let value = visitor.visit_seq(&mut seq)?;
if seq.remaining() == 0 {
Ok(value)
} else {
Err(de::Error::invalid_length(len, &"fewer elements in array"))
}
}

struct Array(std::vec::IntoIter<Value>);
impl Remaining for Array {
fn remaining(&self) -> usize {
self.0.len()
}
}

// `SeqAccess` is provided to the `Visitor` to give it the ability to iterate
// through elements of the sequence.
Expand All @@ -148,6 +174,11 @@ impl<'de> SeqAccess<'de> for Array {
}

struct ArrayRef<'de>(std::slice::Iter<'de, Value>);
impl Remaining for ArrayRef<'_> {
fn remaining(&self) -> usize {
self.0.len()
}
}

// `SeqAccess` is provided to the `Visitor` to give it the ability to iterate
// through elements of the sequence.
Expand Down Expand Up @@ -552,7 +583,7 @@ impl<'de> VariantAccess<'de> for VariantDeserializer {
if v.is_empty() {
visitor.visit_unit()
} else {
visitor.visit_seq(Array(v.into_iter()))
visit_array(Array(v.into_iter()), visitor)
}
}
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Expand All @@ -576,6 +607,8 @@ impl<'de> VariantAccess<'de> for VariantDeserializer {
{
match self.value {
Some(Value::Object(o)) => visitor.visit_map(ObjectAccess::new(o.into_iter())),
// a struct variant may be written as a sequence, as when deserializing from text
Some(Value::Array(a)) => visit_array(Array(a.into_iter()), visitor),
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Some(other.value_type()),
Expand Down Expand Up @@ -610,7 +643,7 @@ impl<'de> de::Deserializer<'de> for &'de Value {
#[allow(clippy::useless_conversion)] // .into() required by ordered-float
Value::Static(StaticNode::F64(n)) => visitor.visit_f64((*n).into()),
Value::String(s) => visitor.visit_borrowed_str(s),
Value::Array(a) => visitor.visit_seq(ArrayRef(a.as_slice().iter())),
Value::Array(a) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
}
}
Expand Down Expand Up @@ -651,7 +684,7 @@ impl<'de> de::Deserializer<'de> for &'de Value {
{
match self {
// Give the visitor access to each element of the sequence.
Value::Array(a) => visitor.visit_seq(ArrayRef(a.as_slice().iter())),
Value::Array(a) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Value::Object(o) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
other => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Expand Down Expand Up @@ -755,7 +788,7 @@ impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
if v.is_empty() {
visitor.visit_unit()
} else {
visitor.visit_seq(ArrayRef(v.as_slice().iter()))
visit_array(ArrayRef(v.as_slice().iter()), visitor)
}
}
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Expand All @@ -779,6 +812,8 @@ impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
{
match self.value {
Some(Value::Object(o)) => visitor.visit_map(ObjectRefAccess::new(o.iter())),
// a struct variant may be written as a sequence, as when deserializing from text
Some(Value::Array(a)) => visit_array(ArrayRef(a.as_slice().iter()), visitor),
Some(other) => Err(crate::Deserializer::error(ErrorType::Unexpected(
Some(ValueType::Object),
Some(other.value_type()),
Expand Down
115 changes: 115 additions & 0 deletions src/tests/serde.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1212,3 +1212,118 @@ fn overdriven_next_key_seed_errors_instead_of_oob() {
let mut input = br#"{"a":1}"#.to_vec();
assert!(from_slice::<Evil>(&mut input).is_err());
}

#[test]
fn value_fixed_length_sequences_reject_extra_elements() {
// From a Value, a tuple/array/struct visitor that stops early used to leave the rest of the
// array unread without error: `[1,2,3]` as `(u8, u8)` gave `(1, 2)`.
use crate::serde::{
from_borrowed_value, from_owned_value, from_refborrowed_value, from_refowned_value,
};
#[derive(Deserialize, Debug, PartialEq)]
struct Pair(u8, u8);
#[derive(Deserialize, Debug, PartialEq)]
struct Named {
a: u8,
}
let mut d = b"[1,2,3]".to_vec();
let o = to_owned_value(&mut d).expect("valid");
let mut d2 = b"[1,2,3]".to_vec();
let b = to_borrowed_value(&mut d2).expect("valid");
assert!(from_owned_value::<(u8, u8)>(o.clone()).is_err());
assert!(from_refowned_value::<[u8; 2]>(&o).is_err());
assert!(from_borrowed_value::<Pair>(b.clone()).is_err());
assert!(from_refborrowed_value::<Named>(&b).is_err());
assert!(from_owned_value::<Named>(o.clone()).is_err());
Comment thread
Licenser marked this conversation as resolved.
// exact length and Vec are unchanged; fewer elements still an error
assert_eq!(from_refowned_value::<Vec<u8>>(&o).ok(), Some(vec![1, 2, 3]));
assert_eq!(
from_owned_value::<(u8, u8, u8)>(o.clone()).ok(),
Some((1, 2, 3))
);
assert!(from_owned_value::<(u8, u8, u8, u8)>(o).is_err());
}

#[test]
fn value_struct_variant_from_sequence() {
// A struct variant written as a sequence deserializes from text; from a Value it failed with
// Unexpected(Object, Array).
use crate::serde::{
from_borrowed_value, from_owned_value, from_refborrowed_value, from_refowned_value,
};
#[derive(Deserialize, Debug, PartialEq)]
enum E {
S { a: u8, b: String },
}
let expected = E::S {
a: 5,
b: "k".to_string(),
};
let mut d = br#"{"S":[5,"k"]}"#.to_vec();
assert_eq!(
from_slice::<E>(&mut d).ok(),
Some(E::S {
a: 5,
b: "k".to_string()
})
);
let mut d = br#"{"S":[5,"k"]}"#.to_vec();
let o = to_owned_value(&mut d).expect("valid");
assert_eq!(
from_owned_value::<E>(o.clone()).ok(),
Some(E::S {
a: 5,
b: "k".to_string()
})
);
assert_eq!(
from_refowned_value::<E>(&o).ok(),
Some(E::S {
a: 5,
b: "k".to_string()
})
);
let mut d = br#"{"S":[5,"k"]}"#.to_vec();
let b = to_borrowed_value(&mut d).expect("valid");
assert_eq!(
from_borrowed_value::<E>(b.clone()).ok(),
Some(E::S {
a: 5,
b: "k".to_string()
})
);
assert_eq!(from_refborrowed_value::<E>(&b).ok(), Some(expected));
for bad in [&br#"{"S":[5]}"#[..], br#"{"S":[5,"k",1]}"#] {
let mut d = bad.to_vec();
let o = to_owned_value(&mut d).expect("valid");
assert!(from_owned_value::<E>(o.clone()).is_err());
assert!(from_refowned_value::<E>(&o).is_err());
}
}

#[test]
fn value_tuple_variant_from_sequence() {
// A tuple variant from a Value reads exactly its elements: extra elements are an error.
use crate::serde::{
from_borrowed_value, from_owned_value, from_refborrowed_value, from_refowned_value,
};
#[derive(Deserialize, Debug, PartialEq)]
enum E {
Tpl(u8, u8),
}
let mut d = br#"{"Tpl":[1,2]}"#.to_vec();
assert_eq!(from_slice::<E>(&mut d).ok(), Some(E::Tpl(1, 2)));
let mut d = br#"{"Tpl":[1,2]}"#.to_vec();
let o = to_owned_value(&mut d).expect("valid");
assert_eq!(from_refowned_value::<E>(&o).ok(), Some(E::Tpl(1, 2)));
assert_eq!(from_owned_value::<E>(o).ok(), Some(E::Tpl(1, 2)));

let mut d = br#"{"Tpl":[1,2,3]}"#.to_vec();
let o = to_owned_value(&mut d).expect("valid");
let mut d2 = br#"{"Tpl":[1,2,3]}"#.to_vec();
let b = to_borrowed_value(&mut d2).expect("valid");
assert!(from_owned_value::<E>(o.clone()).is_err());
assert!(from_refowned_value::<E>(&o).is_err());
assert!(from_borrowed_value::<E>(b.clone()).is_err());
assert!(from_refborrowed_value::<E>(&b).is_err());
}
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